The present disclosure generally relates to apparatus and methods for treatment of spinal disorders using an intervertebral prosthesis which is disposed in an intervertebral space (or cavity) following removal of a damaged or diseased intervertebral disc.
The bones and connective tissue of an adult human spinal column consists of more than twenty discrete bones coupled sequentially to one another by a tri-joint complex. Each tri-joint complex includes an anterior disc and two posterior facet joints. The anterior space between adjacent bones are cushioned by cartilage spacers referred to as intervertebral discs. These more than twenty bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine, which comprises the top of the spine, up to the base of the skull, includes the first seven vertebrae. The intermediate twelve bones are the thoracic vertebrae, and connect to the lower spine comprising the five lumbar vertebrae. The base of the spine includes the sacral bones (including the coccyx). The component bones of the cervical spine are generally smaller than those of the thoracic spine, which are in turn smaller than those of the lumbar region. The sacral region connects laterally to the pelvis.
The spinal column is highly complex in that it includes these more than twenty bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these conditions, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.
Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the factors that can result in spinal pathologies for which surgical intervention may be necessary. A variety of systems have been disclosed in the art that achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determines the appropriate surgical protocol and implantation assembly. The spine surgical community has accepted intervertebral devices (commonly known as interbody spacers, and allograft transplants) as part of the state of the art and routine practice employs such devices in the reconstruction of collapsed inter-vertebral disc spaces.
Surgeons insert these intervertebral devices to facilitate bone fusion in between and into the contiguous involved vertebrae. This fusion creates a new solid bone mass, which acts to hold the spinal segment at an appropriate biomechanically restored height as well as to stop motion in a segment of the spine in which the patient is experiencing pain. Items surgically placed in these involved interbody regions can thus stimulate interbody bone in-growth such that the operated anterior spinal segments heal into a contiguous bone mass; in other words, a fusion occurs. Further, the surgical community uses such man-made implants or biological options to provide weight bearing support between adjacent vertebral bodies, and thereby correct or alleviate a variety of clinical problems. In this regard, surgeons use intervertebral spinal implants/transplants for surgical therapy for degenerative disc disease (DDD), discogenic low back pain, spondylolisthesis, reconstruction following tumor or infection surgery, and other spine related maladies requiring surgical intervention.
In many implant designs, a relatively hard or sturdy implant construct is formed from a selected biocompatible material such as metal, ceramic, or carbon fiber-reinforced polymer. This implant construct often has a partially open or porous configuration and is coated or partially filled with a selected bone ingrowth-enhancing substance, such as harvested bone graft supplied from the patient, human donor allograft bone transplant material supplied by a tissue bank, genetically cultivated bone growing protein substitutes, and/or other biological/biochemical bone extenders. Such devices, when implanted into the intervertebral space, promote ingrowth of blood supply and grow active and live bone from the adjacent spinal vertebrae to inter-knit with the implant, thereby eventually immobilizing or fusing the adjacent spinal vertebrae. Such implants also commonly include a patterned exterior surface such as a ribbed or serrated surface, or screw thread geometry, to achieve enhanced mechanical locking with the adjacent vertebrae during the bone ingrowth/fusion process.
With respect to the failure of the intervertebral disc, the interbody fusion cage has generated substantial interest because it can be implanted laparoscopically into the anterior of the spine, thus reducing operating room time, patient recovery time, and scarification. Conventional intervertebral body cages generally comprise a tubular metal body having an external surface threading. They are inserted transverse to the axis of the spine, into preformed cylindrical holes at the junction of adjacent vertebral bodies. The cages include holes through which the adjacent bones are to grow. Additional materials, for example autogenous bone graft materials, may be inserted into the hollow interior of the cage to incite or accelerate the growth of the bone into the cage.
There are several commercially available devices that operate as stand-alone (that is, without support from an additional construct such as an anterior plate and screws, or posteriorly placed screws and/or rods placed into the pedicles or facet joints) interbody fusion devices. These devices include the Stalif™, SynFix™, and the VerteBridge™. The Stalif™ is a device for the fusion of the lumbar spine. The implant is inserted and fixed via diverging screws passing through pre-drilled apertures of the device that penetrate into the vertebral bodies. The screws are manually placed into the apertures of the device and are driven using an appropriate tool, such as a surgical screw driver. The Stalif™ is available from Surgicraft Limited Corporation, 16 The Oaks Clews Road Redditch, United Kingdom (www.surgicraft.co.uk). The SynFix™ is also a device that is placed in an intervertebral space and fixed via diverging screws passing through the device and into the vertebral bodies. Again, the screws are manually placed into the apertures of the device and are driven using a surgical screw driver. The SynFix™ is available from Synthes, Inc., 1302 Wrights Lane East, West Chester, Pa. 19380 (www.synthes.com) The VerteBridge™ is a device for the fusion of the spine in which anchoring blades are press-driven (using a specialized tool) through apertures in the device and into the respective vertebral bodies to fix the device in place. The VerteBridge™ is available through the LDR Spine (www.ldrholding.com).
All of the above-described devices have an anchor which is secondarily added to the initial device. The Stalif™ and SynFix™ devices employ screws while the VerteBridge™ utilizes a blade anchor. Both the Stalif™ and SynFix™ devices require the screws to be inserted at trajectories that are difficult to achieve given common human anatomical structures, especially at the spinal level L5-S1. Additionally, the proximal end of the screws may protrude anteriorly, causing potential irritation to the great vessels. The VerteBridge™ has a pair of blades inserted after the initial device is put in place. The blades are supposed to flex enough to curve within the device, and to exhibit sufficient strength to cut through bone. These blades, although flexible, need to be able to hold the vertebral bodies in place. In practice, these features are not always achieved.
A number of devices have been developed, which employ self-contained anchoring elements that are deployed after the device is placed into the intervertebral space. For example, U.S. Patent Application Pub. No. 2006/0241621 (incorporated herein in its entirety) discloses a device for joining intervertebral members together using a self-drilling screw apparatus. The screw apparatus includes a shell and first and second screw members having tapered ends and threaded bodies that are disposed within the shell. A drive mechanism rotatably drives the first and second screw members from the shell in precisely co-axial, opposite directions, which causes the screw members to embed themselves in the vertebral bodies. U.S. Pat. No. 5,800,550 (incorporated herein in its entirety) discloses a device for joining intervertebral members together using a self-deploying pair of posts. The apparatus includes a body and first and second post members that are disposed within the body. A drive mechanism press-drives the first and second posts from the body in precisely co-axial, opposite directions (longitudinally aligned with the spine), which causes the posts to embed themselves in the vertebral bodies. The problems with these devices include that the co-axial, opposite deployment of the screws/posts is not an ideal configuration for fixing an intervertebral device. Indeed, such a deployment may permit slippage of the device during or after deployment because of the natural stresses applied to the device from the patient's anatomical spinal structures.
Given the disadvantageous features of the prior art devices, there is a need for a new intervertebral device that includes self-contained anchoring members that deploy in desirable transverse directions.